Centrifuge with sludge level sensing means

ABSTRACT

The centrifugal rotor has a sludge-accumulating space from which an indicating channel extends inwardly to the region of the rotor axis. Clogging of the outer end of this channel by sludge is sensed by a device comprising a pressure signal amplifier, a pressure differential gage, a pressure-transmitting connection between one side of the amplifier and one side of the gage, a connection for transmitting a pressure of the liquid being separated, and a connection for transmitting a pressure of the liquid in the indicating channel, one of said last two connections leading to the other side of the amplifier and the other of said last two connections leading to the other side of said gage. Thus, the arrangement provides a measure of the difference between the pressure of the indicating liquid and the pressure of the separated liquid.

United States Patent Nilsson 1 Feb. 15, 1972 i [54] CENTRIFUGE WITHSLUDGE LEVEL 3,396,910 8/1968 Steinacker ..233/l4 R SENSING MEANS3,081,027 3/1963 Coulson 2,628,023 2/1953 Dahlstedt ..233/l9 R [72]Inventor: Vilgot Raymond Nilsson, Hagersten,

Swede" Primary Examiner-Jordan Franklin Assistant Examiner-George H.Krizmanich [73] Asslgnee. Alta Laval AB, Tumba, Sweden Atmmey DavisHoxie Faithful & pg [22] Filed: May 4, 1970 [2]] Appl. No: 34,208 I [57]ABS CT The centrifugal rotor has a sludge-accumulating space from whichan indicating channel extends inwardly to the region of [30] FomgnAppnwmn Pnomy Data the rotor axis. Clogging of the outer end of thischannel by May 8, 1969 Sweden ..6Sl3/69 sludge is sensed by a devicecomprising a pressure signal plifier, apressure differential gage, apressure-transmitting 52 US. (:1. ..233/19 A, 210/371 connection betweenone Side of the amplifier and one side of 511 rm. (:1 .3041; 1 1 thegage a connection for transmitting a Pressure of the liquid 58 Field ofSearch ..23 3/19 R, 19 A, 14 R, 14A, being SePamed, and a wmcfimtransmitting a Pressure 2 3/20 R 20 210/104 05 3 9 370 371 ofthe liquidin the indicating channel, one Of last tWO COH- nections leading to theother side of the amplifier and the i 56] References Cited other of saidlast two connections leading to the other side of said gagev Thus, thearrangement provides a measure of the UNITED TES PATENTS differencebetween the pressure of the indicating liquid and the pressure of theseparated liquid. 3,408,000 10/1968 Nilson ..233/l9 R 3,494,545 2/1970Nilson ..233/19 R 4 Claims, 4 Drawing Figures itea I 24 7 -20 2 a 2 K"'2 i l0 a u 1 12 t H 7 s I SHEET 1 BF 4 PATENTEU FEB 1 5 I972 INVENTOR.VlLG-OT RA YMOND NILSSON 3W mrnusvs PATENTEDFEB 15 I972 SHEET 2 0F 4 fK. 3. 2 uwmumwww INVENTOR. VILGOT RR YMOND NILSSON QM, H ui Ua mPATENTEDFEBISIQTZ 3.642.196 saw u (1r 4 Liquid Pressure hrougpuf ofLiquidBeing SeparaIed I N VIz'N 'I'OR VII-GOT RR YNOND NILSS 0CENTRIFUGE WITH SLUDGE LEVEL SENSING MEANS The present invention relatesto a centrifuge having an outlet for separated liquid and a means forindicating the sludge level in the sludge space of the rotor, such meanscomprising an indicating channel extending from the sludge spaceinwardly to the axis of the rotor and rotating therewith, and a deviceconnected to this channel for sensing clogging of the opening of thechannel into the sludge space with sludge.

In centrifuges of this kind, the sludge level indicating signal,generated by the clogging of the indicating channel with sludge, hasbeen based upon sensing the absolute pressure in the sludge space.Consequently, this signal is not always due to the formation of adefinite sludge level but may also be influenced by changes in theliquid pressure in the separating space, such as may occur with changesin the supply of liquid to be separated or changes in thecounterpressure in the outlet for the separated liquid. According toSwedish Pat. No. 213,945, ,it has been proposed to eliminate thesesignaldisturbing factors by an arrangement of two indicating channels,the outer openings ofwhich are situated at different radial distancesfrom the axis of rotation. Thus, there is sensed only that pressurechange which is caused by the sludgeclogging of one of the twoindicating channels. However, this solution requires that each of thetwo indicating channels be connected to a corresponding stationarypipeline situated outside the centrifuge rotor. If the centrifuge is ofa closed type so that these connections are hermetic and require sealingrings, it is necessary to make one of the sealing rings of thecentrifuge with an extra large diameter, which has caused wearingproblems- If the centrifuge is provided with a paring device serving asthe outlet for the separated liquid, and the indicating channel is alsoconnected to a paring device, the arrangement of a plurality of paringchambers causes space problems.

According to the present invention, these disadvantages are avoidedwhile maintaining the sludge level sensing device unaffected by theaforesaid signal-disturbing factors, in a centrifuge of the kindpreviously described. More particularly, the sensing device comprises apressure signal amplifier, a pressure difference gage, apressure-transmitting connection between one side of the amplifier andone side of the gage, a connection for transmitting a pressure of theliquid being separated, and a connection for transmitting a pressure ofthe liquid in the indicating channel, one of these last two connectionsleading to the other side of the amplifier and the other connectionleading to the other side of the gage. The pressuretransmittingconnections can be hydraulic, pneumatic or electrical.

The invention can be utilized in centrifuges of either the open type orthe closed type. In centrifuges having hermetically connected inlets andoutlets, and also in centrifuges having an overflow outlet fordischarging the separated liquid, the connection for transmitting apressure of the liquid being separated can be connected to thecentrifuge inlet. In centrifuges having a paring device for dischargingthe separated liquid, this same connection can be connected to thecentrifuge inlet if a valve for maintaining a constant pressure isinserted in the outlet channel of the paring device. According to apreferred embodiment of the invention, which is simple from aconstructional point of view and can be used in open as well as inclosed centrifuges, the connection for transmitting a pressure of theliquid being separated is connected to the outlet for the separatedliquid. Pneumatic pressure-transmitting connections are preferred so asto actuate the pressure signal amplifier and the pressure differencegage in a harmless way. Hydraulic transmission of the pressure signalsto these devices can be harmful to their pressure-actuated instruments.

The invention is described more in detail below with reference to theaccompanying drawings, in which FIGS. 1, 2 and 3 are axial sectionalviews of different embodiments of the present centrifuge, and FIG. 4 isa diagram showing the pressure of the liquid being separated and that ofthe indicating liquid in dependence of the throughput of the liquidbeing separated.

In FIG. 1, the centrifuge rotor 1 has a cover 2 which is held fast tothe part 1 by means ofa locking ring 3. The rotor is carried and drivenby a shaft 4 which is provided with a central channel 5 for the supplyof a sludge-containing liquid to be separated. This liquid is led by adistributor 7, provided with radial entraining vanes 6, into theseparating chamber 8. The latter contains a set of conical discs 9.Sludge l0 separated from the liquid is collected at the periphery of theseparating chamber and is discharged intermittently through openings 11in the rotor body 1. These openings are alternately uncovered and closedby a valve piston 12, the movements of which are effected in aconventional manner by means of a liquid from a cylindrical supply duct13 surrounding the shaft 4. The piston 12 is pressed upward against thecover 2 to close the sludge outlets 11 when liquid is supplied from duct13 to a space 14 below the piston, a certain outflow of this liquidtaking place at the same time through drain holes 15. The piston ispressed downward by the liquid pressure in the separating space 8 whenthe liquid supply through the duct 13 is interrupted, since the liquidis then drained from the space 14 through the holes 15.

Separated liquid flows from the inner edge of the disc set 9 to a paringchamber 16, in which there is mounted a stationary paring disc 17 whichdischarges separated liquid through an outlet pipe 18. The indicatingchannel 19 may be formed by one or more radially extending tubes or by adisc interspace which is divided by radially extending ridges, it beingassumed that the section in the left-hand part of FIG. I is takenthrough such a ridge. The radially inner end of the indicating channel19 opens into a paring chamber 20 in which there is mounted a stationaryparing disc 21 connected to a discharge pipeline 22. The level of theseparated liquid is shown at 23, and the level of the indicating liquidis shown at 24.

On the outlet pipe 18 there is mounted a diaphragm housing 25, thediaphragm of which is subjected on one'side to the liquid pressure inthe outlet pipe 18. The other side of this diaphragm is subjected to thepressure of air which is blown into a pipeline 26 connecting thediaphragm housing to one side of a pressure signal amplifier 27 of aconventional type. The air is blown into the pipeline 26 through abranch pipe 28. That part of the diaphragm housing 25 to which the airpipeline 26 leads has a throttled outlet hole (not shown) to theatmosphere, thus providing a conventional arrangement whereby the airpressure in pipeline 26 varies inaccordance with variations of theliquid pressure in outlet pipe 18. The pipeline 22 is in turn connectedby duct 22a to one 'side' of a pressure differential gage 29, also of aconventional type, and air is blown into the duct 22a through a pipeindicated by an arrow 30. The pressure difference gauge 29 is providedwith an electric switch 31 shown schematically in the drawing. The otherside of the signal amplifier 27 has a pneumatic connection 32 to theother side of the pressure difference gage 29. In principle, thisconnection can be hydraulic or electric instead of pneumatic. The signalamplifier 27 is provided with an adjustment screw 33 for changing theamplification degree, and the pressure difference gage 29 is providedwith an adjustment screw 34 for adjusting the pressure difference towhich the gage will react. The indicating channel 19 is provided with aleakage hole 35 which is necessary for the generation of the sludgeclogging signal. In principle, the amplifier 27 and the gage 29 canchange places with each other.

In operation, the air blown in through the pipelines 30 and 22 flowsthrough the paring disc 21 and into the paring chamber 20, where itpasses through the liquid before reaching the atmosphere. The positionof the liquid 1 vel 24 corresponds to the counterpressure which the airmee s in its outflow, and this counterpressure actuates the pressuredifference gage 29 via the pipeline 22-220. The pressure of theseparated liquid discharged by the paring disc 17 and pipe 18corresponds to the position of the liquid level 23 and acts upon thelower side of the diaphragm in housing 25, and the upper side of thisdiaphragm is acted upon by air blown in through the pipelines 28 and 26.This air leaks out through the aforementioned throttled hole in thediaphragm housing wall and subjects the signal amplifier 27 via thepipeline 26 to an air pressure corresponding to the separated liquidpressure in' pipe 18. Thus, the pressure of the separated liquidactuates the signal amplifier pneumatically. The pressure signalreceived by the signal amplifier is transmitted, after an amplificationadjusted by means of the screw 33, to the pressure difference gage 29via the pipeline 32. When sludge clogs the opening of the channel 19into the sludge space, the liquid level 24 moves radially outward due toleakage through the hole 35, so that the air flowing out through theparing disc 21 meets a reduced counterpressure. This means that thepressure difference gage 29 via the pipeline 2222a is acted upon by areduced pres sure and senses an increased difference between thepressure of the indicating liquid and that of the separated liquid. Whenthis difference corresponds to the difference for which the screw 34 isadjusted empirically, the electric switch 31 is actuated to initiate asludge discharge by conventional means (not shown). The influence ofvariations in the supply of the liquid to be separated or in thecounterpressure of the discharging separated liquid on the sludgeclogging signal is eliminated, since the absolute pressure of theindicating liquid is not measured but rather the difference between thepressure of the indicating liquid and that of the separated liquid (inother words, the difference between the levels 24-and 23 of theseliquids).

According to FIG. 2, in which corresponding details have the samereference numerals as in FIG. 1, the pipeline 18 is hermeticallyconnected to the rotor by means ofa seal 36, and the pipeline 22hermetically connected to the inner end of the indicating channel 19 bymeans of a seal 37. This channel end has the form of a central space 38into which the pipeline 22 opens. The other end of the pipeline 22 opensinto a diaphragm housing 25a, and the continuation of the pipeline 22 tothe pressure difference gage 29 is designated at 22a.

The arrangement according to FIG. 2 functions in principle in the sameway as the arrangement according to FIG. 1. The difference is only thatin the embodiment according to FIG. 2, a reduction of the pressure inthe space 38 is sensed when a sludge plug has been formed atthe outerend of the channel 19.

In FIG. 3, showing part of an axial section of still another embodimentof the present centrifuge, the reference numeral 41 designates the rotorcontaining a set of conical discs 42, a distributor 44 and an indicatingchannel 45, the radially outer opening of which is located in the sludgespace of the rotor. The sludge-containing liquid is supplied to therotor through a stationary central inlet pipe 43, and a stationaryparing disc 46 is provided for the discharge of the separated liquid. Achannel 47 leads from the inner edges of the discs 42 to a paringchamber 48 containing the paring disc 46. The channel 45 opens at itsradially inner end into a paring chamber 49, in which are provided twostationary paring discs 50 and 51. The lower paring disc 50 leads theliquid, pared by this disc, through the distributor 44 back to theseparating chamber of the rotor.

The parts 25 to 34 in FIG. 3 are the same as those in FIG. 1. Thus, thediaphragm housing 25 is mounted on the outlet pipeline of the paringdisc 46, and through the air blown in at the level of the indicatingliquid in the paring chamber 49 is sensed, which sensing takes place inthe pressure difference gage 29. For the rest, the parts 25 to 34function in the same way as those in the embodiment according to FIG. 1.The paring disc 50 corresponds in its effect to the leakage hole in FIG.1 and thus accommodates the displacement of the liquid level in theparing chamber 49 radially outward when a sludge plug has been formed inthe outer end of the indicating channel45.

The diagram according to FIG. 4 has for its purpose to explain the dutyof the pressure signal amplifier-27. Owing to the fact that the flowchannels of the liquid to be separated and the indicating liquid ontothe pressure-sensing means have different flow resistances, a pressurechange in the one liquid will not correspond to an equally greatpressure change in the other liquid, calculated in absolute measures,during the separation periods between the sludge cloggings of theindicating channel. However, since the relationship between the pressureof each of the two liquids and the throughput of the liquid beingseparated, in the diagram according to FIG. 4, forms a straight line, itis possible to eliminate the divergence of the pressure changes so thatthe two relationship lines are made parallel or coincident. According tothe invention, this is effected by means of the pressure signalamplifier 27. In FIG. 4, in which it is assumed that the relationshiplines start from the origin (although it is not necessary that this bethe case), the throughput of the liquid being separated is traced on theabscissa and the liquid pressure on the ordinate. The line a is assumedto designate the relationship line of the indicating liquid and the lineb the relationship line of the liquid being separated. By turning theadjustment screw 33 of the signal amplifier 27, the line b can be ineffect turned around the origin such that the line b will coincide withthe line a. If the two lines a and b do not cut any of the coordinatelines in the same point, the lines a and b can be caused to becomeparallel by turning the screw 33. This, however, gives the same desiredresult.

It will be observed that in FIG. 3 the inlet pipe 43 constitutes astationary duct connected to the rotor inlet, the paring disc 46constitutes a stationary duct leading from the rotor outlet for theseparated liquid, and leading from the rotor outlet via disc 46 is aconnection including the parts 25-26 for transmitting pneumatically toamplifier 27 a pressure of the liquid being separated. It will also beobserved that air blown in at 30 (FIG. 1) enters both of the pipelines22 and 2211, so that the latter line is strictly pneumatic. The line 22,on the other hand, contains liquid at a level depending upon the liquidlevel 24 and through which air is forced downward into paring chamber 20as previously described.

I claim:

1. In combination with a centrifuge comprising a centrifugal rotorhaving an inlet for sludge-containing liquid and also having an outletfor separated liquid and a sludge space for accumulating separatedsludge, the rotor being provided with an indicating channel extendingfrom said sludge space inwardly to the region of the rotor axis androtating with the rotor, a device connected to said channel for sensingwhen sludge clogs the opening of the channel into the sludge space, saiddevice comprising a pressure signal amplifier, a pressure differentialgage, a pressure-transmitting connection between one side of theamplifier and one side of the gage, a connection for transmitting apressure of the liquid being separated to one of said amplifier andgage, and a connection for transmitting to the other of said amplifierand gage a pressure of the liquid in the indicating channel, one of saidlast two connections leading to the other side of the amplifier and theother of said last two connections leading to the other side of saidgage.

2. The combination according to claim 1, comprising also stationaryducts connected to said rotor inlet and outlet, respectively, saidconnection for transmitting a pressure of the liquid being separatedbeing connected to the rotor outlet.

3. The combination according to claim 1, in which said con nection fortransmitting a pressure of the liquid is separated being connected tosaid rotor outlet for the separated liquid.

4. The combination according to claim 1, in which saidpressure-transmitting connections are pneumatic. l

1. In combination with a centrifuge comprising a centrifugal rotorhaving an inlet for sludge-containing liquid and also having an outletfor separated liquid and a sludge space for accumulating separatedsludge, the rotor being provided with an indicating channel extendingfrom said sludge space inwardly to the region of the rotor axis androtating with the rotor, a device connected to said channel for sensingwhen sludge clogs the opening of the channel into the sludge space, saiddevice comprising a pressure signal amplifier, a pressure differentialgage, a pressure-transmitting connection between one side of theamplifier and one side of the gage, a connection for transmitting apressure of the liquid being separated to one of said amplifier andgage, and a connection for transmitting to the other of said amplifierand gage a pressure of the liquid in the indicating channel, one of saidlast two connections leading to the other side of the amplifier and theother of said last two connections leading to the other side of saidgage.
 2. The combination according to claim 1, comprising alsostationary ducts connected to said rotor inlet and outlet, respectively,said connection for transmitting a pressure of the liquid beingseparated being connected to the rotor outlet.
 3. The combinationaccording to claim 1, in which said connection for transmitting apressure of the liquid is separated being connected to said rotor outletfor the separated liquid.
 4. The combination according to claim 1, inwhich said pressure-transmitting connections are pneumatic.